An original email message and a chain or thread of related reply messages or forwarded messages can be grouped as a conversation. The embedded attributes (e.g., header information) of a message contain a unique identifier and a chain of message identifiers which can be used to relate the message to replies and forwards. Grouping messages into conversations based upon references in a message's header information alone can be unreliable. Users will often use an existing message, deleting the subject and content, to start a new conversation while being unaware that the header information is still embedded in the message. Additionally, the inclusion of header information is optional and, as a result, not all messages include header information. Reliance on header information alone is over-inclusive in the first scenario and under-inclusive in the second scenario.
Furthermore, reply messages often also include or quote text from the original message or the message to which it is replying. Once messages are grouped into a conversation, this text is often redundant and can be lengthy and distracting.